Cameron offers Tories credibility

His "invitation to join the government of Britain" also offers a belated contrast to Labour's top-down, and overly bureaucratic, approach where success is judged by the amount of money spent rather than the quality of the end product.

Mr Cameron is also right on another recurring theme of his "big society'' manifesto. Responsibility does not just apply to government. It extends to every individual and, by working together, the talents of the whole nation can be harnessed to create a smaller, and more effective state, with local involvement the critical component. This was the clearest indication yet of how the Tories differ from Labour.

The challenge for the Conservative leader now is still formidable: he needs to show voters how his grassroots revolution will work in practice, and how it can still be applied when the next government will, from day one, be bogged down by a record deficit.

This is far more important than Mr Cameron, and his colleagues, perpetuating the negative campaigning that has been such an unwelcome feature of this election thus far. People are all too aware, from their own personal financial situation, about Gordon Brown's record, and the risks involved with re-electing Labour. They are too intelligent to need reminding about this on an hourly basis.

What they want to know is how this devolved approach will work on a day-to-day basis, especially when so many local authorities are bywords for profligacy and inefficiency, and how the Tories intend to tackle the great social challenges, like pensions and care for the elderly, that have festered under New Labour.

Equally, they want to know whether the Tory plans are affordable, while also leaving sufficient scope for lower taxes to help accelerate Britain's recovery.

It is in Mr Cameron's interests that he now makes, and wins, this positive argument. For, if he does, he will have gained a deserved mandate to bring about change – rather than being elected simply because the Conservatives offered the "least worst" option.